While most users of Microsoft Windows-based PCs have seen their systems lockup and display the dreaded 'blue screen of death,' a new, lavender-hued variant of the problem has emerged.

The so-called "purple screen of death" occurs when there's a conflict between certain system drivers and Windows Vista's Desktop Window Manager, according to researchers at NeoSmart -- a nonprofit technology tracking firm that first spotted the issue.

When the glitch occurs, windows on the Vista desktop turn purple and become unresponsive, according to NeoSmart. "It's caused by a low-level problem in the kernel, and it does make you want to restart your PC," NeoSmart researchers said in a blog post on the subject.

NeoSmart concedes that the problem is rare, and that most Vista users probably haven't encountered it. "It's something to do with the way the Windows Vista kernel handles a certain exception in the graphics driver subsystem."

One poster on the NeoSmart blog said he was hit with the 'purple screen of death' while his computer was equipped with Nvidia graphics drivers that had not yet been optimized for Vista. "It creeped me out... I mean, why purple, of all colors!?," wrote Mark Anders.

While the "purple screen of death" seems rare and not terribly serious, the system conflict behind the problem is the latest example of the almost innumerable issues that software makers face when rolling out major product upgrades.

Mac users have reported that Apple's new Leopard OS is itself subject to the "blue screen of death" -- a major system crash that previously was confined mostly to Microsoft operating systems.

Part of the problem is that, in their efforts to outdo each other, Apple and Microsoft are loading literally hundreds of new features into their latest offerings -- and testing all of them in all conceivable usage scenarios would be costly and impractical.

In the end, most software makers rely on post-release service packs to fix problems that emerge after a product has shipped. Service Pack 1 for Windows Vista is currently undergoing beta testing.